System and method for exhaust heat generation using electrically actuated cylinder valves and variable stroke combustion cycles

ABSTRACT

A method for operating an engine having at least a first and second cylinder, including operating the first cylinder with a spark timing more retarded than a spark timing of a second cylinder; and operating one of said first cylinder and second cylinders with a first number of strokes per cycle different from other cylinders of the engine for at least one combustion cycle.

FIELD

The present description relates to a method for controlling enginecylinder valve operation.

BACKGROUND AND SUMMARY

Vehicles with internal combustion engines use catalytic converters toconvert exhaust constituents and reduce regulated emissions. However, insome converters, conversion efficiency can be low at ambienttemperatures. As such, various approaches have been used to increaseexhaust heat during engine starting to thereby obtain earlier increasedconversion efficiency.

One such approach is described in U.S. Pat. No. 6,725,830, which usesdifferent ignition timing in different cylinder groups to increase totalexhaust heat to the catalyst/exhaust, while still providing accurateidle speed control, among other features. In one example, the ignitiontiming of one group is significantly retarded after top dead center sothat little torque is produces, but large quantities of heat areproduced. Then, the remaining cylinders operate at higher load, whichalso increases exhaust heat, while retaining accurate torque control.

However, the inventors herein have recognized that under someconditions, depending on the engine firing order exhaust mixing and heatgeneration may be somewhat degraded. For example, depending on engineconfiguration, the firing order may pair some cylinders with the sameignition timing and others with disparate timings. While such operationmay be used to reduce vibration under some conditions, there are otherconditions where such operation may result in less even exhaust heatingand less quantity of exhaust heat transferred to the emission controlsystem devices.

As such, in one aspect, a method for operating an engine having at leasta first and second cylinder, comprising: operating the first cylinderwith a spark timing more retarded than a spark timing of a secondcylinder; and operating one of said first cylinder and second cylinderswith a first number of strokes per cycle different from other cylindersof the engine for at least one combustion cycle.

In this way, it is possible to change a combustion firing order toenable improved exhaust gas heating with cylinders having disparateignition timing, at least under some conditions. In one example, atleast one cylinder can be operated with a different number of strokes tovary the combustion firing order until a desired firing order isreached. In another example, multiple cylinders can be operated withvarying numbers of strokes to achieve a new firing order. In still otherexample, cylinders can have the number of strokes of their combustioncycle sequentially varied until a desired firing order is reached.

Another advantage of the above operation is that in some cases, acylinder can operate with a decreased number of strokes per combustioncycle, thereby further increasing heat flux to the exhaust. For example,cylinders with more ignition timing retard can be operated with atwo-stroke combustion cycle, thereby about doubling the amount of heatflux to the exhaust from those cylinders and thus obtain faster catalysttemperature increases.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an engine;

FIG. 2 is a schematic diagram of an engine valve;

FIGS. 3-4 are example engine and valve configurations;

FIGS. 5-7 are high level flow charts illustrating various aspects ofcontrol routines; and

FIGS. 8-11 are engine timing diagrams illustrating various exampleembodiments.

DETAILED DESCRIPTION

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 an exhaust valve 54. Each intake and exhaustvalve is operated by an electromechanically controlled valve coil andarmature assembly 53, such as shown in FIG. 2. Armature temperature isdetermined by temperature sensor 51. Valve position is determined byposition sensor 50. In an alternative example, each of valves actuatorsfor valves 52 and 54 has a position sensor and a temperature sensor. Instill another alternative, one or more of intake valve 52 and/or exhaustvalve 54 may be cam actuated, and be capable of mechanical deactivation.For example, lifters may include deactivation mechanism for push-rodtype cam actuated valves. Alternatively, deactivators in an overhead cammay be used, such as by switching to a zero-lift cam profile.

Intake manifold 44 is also shown having fuel injector 66 coupled theretofor delivering liquid fuel in proportion to the pulse width of signalFPW from controller 12. Fuel is delivered to fuel injector 66 by fuelsystem (not shown) including a fuel tank, fuel pump, and fuel rail (notshown). Alternatively, the engine may be configured such that the fuelis injected directly into the engine cylinder, which is known to thoseskilled in the art as direct injection. In addition, intake manifold 44is shown communicating with optional electronic throttle 125.

Distributorless ignition system 88 provides ignition spark to combustionchamber 30 via spark plug 92 in response to controller 12. UniversalExhaust Gas Oxygen (UEGO) sensor 76 is shown coupled to exhaust manifold48 upstream of catalytic converter 70. Alternatively, a two-stateexhaust gas oxygen sensor may be substituted for UEGO sensor 76.Two-state exhaust gas oxygen sensor 98 is shown coupled to exhaustmanifold 48 downstream of catalytic converter 70. Alternatively, sensor98 can also be a UEGO sensor. Catalytic converter temperature ismeasured by temperature sensor 77, and/or estimated based on operatingconditions such as engine speed, load, air temperature, enginetemperature, and/or airflow, or combinations thereof.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, andread-only memory 106, random access memory 108, 110 keep alive memory,and a conventional data bus. Controller 12 is shown receiving varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor119 coupled to a accelerator pedal; a measurement of engine manifoldpressure (MAP) from pressure sensor 122 coupled to intake manifold 44; ameasurement (ACT) of engine air amount temperature or manifoldtemperature from temperature sensor 117; and a engine position sensorfrom a Hall effect sensor 118 sensing crankshaft 40 position. In apreferred aspect of the present description, engine position sensor 118produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft from which engine speed (RPM) can bedetermined.

In an alternative embodiment, a direct injection type engine can be usedwhere injector 66 is positioned in combustion chamber 30, either in thecylinder head similar to spark plug 92, or on the side of the combustionchamber. Also, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof.

FIG. 2 shows an example dual coil oscillating mass actuator 240 with anengine valve actuated by a pair of opposing electromagnets (solenoids)250, 252, which are designed to overcome the force of a pair of opposingvalve springs 242 and 244. FIG. 2 also shows port 270, which can be anintake or exhaust port). Applying a variable voltage to theelectromagnet's coil induces current to flow, which controls the forceproduced by each electromagnet. Due to the design illustrated, eachelectromagnet that makes up an actuator can only produce force in onedirection, independent of the polarity of the current in its coil. Highperformance control and efficient generation of the required variablevoltage can therefore be achieved by using a switch-mode powerelectronic converter. Alternatively, electromagnets with permanentmagnets may be used that can be attracted or repelled.

As illustrated above, the electromechanically actuated valves in theengine remain in the half open position when the actuators arede-energized. Therefore, prior to engine combustion operation, eachvalve goes through an initialization cycle. During the initializationperiod, the actuators are pulsed with current, in a prescribed manner,in order to establish the valves in the fully closed or fully openposition. Following this initialization, the valves are sequentiallyactuated according to the desired valve timing (and firing order) by thepair of electromagnets, one for pulling the valve open (lower) and theother for pulling the valve closed (upper).

The magnetic properties of each electromagnet are such that only asingle electromagnet (upper or lower) need be energized at any time.Since the upper electromagnets hold the valves closed for the majorityof each engine cycle, they are operated for a much higher percentage oftime than that of the lower electromagnets.

While FIG. 2 appears show the valves to be permanently attached to theactuators, in practice there can be a gap to accommodate lash and valvethermal expansion.

Referring now to FIG. 3, engine 10 is shown as an example inlinefour-cylinder engine having each cylinder coupled to a common intakemanifold 44 and a common exhaust manifold 48. While this example showseach cylinder coupled to common intake and exhaust manifolds, separateexhaust manifolds for one cylinder, or groups of cylinders, may be used,if desired. One such example is described below herein with regard toFIG. 4.

Continuing with FIG. 3, four cylinders 310, 312, 314, and 316 are shownin an inline configuration. As described below, various other engineconfigurations and numbers of cylinders may be used, if desired. Each ofcylinders 310-316 have four valves per cylinder, labeled a, b, c, and d.Thus, in this example, cylinder 310 has four valves, 310 a, 310 b, 310c, and 310 d. Likewise, cylinder 312 has four valves, 312 a, 312 b, 312c, and 312 d, cylinder 314 has four valves, 314 a, 314 b, 314 c, and 314d, and cylinder 316 has four valves, 316 a, 316 b, 316 c, and 316 d.While this example has four valves per cylinder, various otherconfigurations may be used, such as, for example, three valves percylinder, two valves per cylinder, or combinations thereof.

As shown by FIG. 3, valves with subscript “a” are each in a commonlocation in the cylinder. Likewise, valves with subscript “b” are eachin a common location, and so on with subscripts “c” and “d.”

In the example of FIG. 3, each cylinder valve may be electricallyactuated without the use of a camshaft. Alternatively, some of thecylinder valves may be electrically actuated and some may be camactuated. The cam actuated valves may have fixed cam timing, or may havevariable cam timing. Further, the cam actuated valves may bemechanically deactivated, such as by deactivating a lifter or pushrod,for example.

FIG. 3 shows that each cylinder has two valves coupled to an intake sideof the engine (a, b) and two valves coupled to an exhaust side of theengine (c, d). As noted above, different numbers of valves may be used,for example two intake side valves and a single exhaust side valve.Further, as noted above, some valves, such as intake side valves, can beelectrically actuated, while some valves, such as exhaust side valves,may be cam actuated.

Continuing with the engine of FIG. 3, the cylinders may be groupedtogether into groups 320 and 322, where group 320 includes cylinders 310and 312, and group 322 includes cylinders 314 and 316. This is just oneexample grouping, and the cylinders may be grouped in other ways, ifdesired. For example, cylinders 312 and 314 may be one group, andcylinders 310 and 316 another group. As described below herein, thecylinder groups may be operated in selected configurations to provideimproved engine exhaust heat and improved performance.

Referring now to FIG. 4, an example V-8 engine is shown having eightcylinders 410, 412, 414, 416, 418, 420, 422, and 424. In this example,cylinders 410-416 are in a first bank, and cylinders 418-424 are in asecond bank. While the banks of the engine may constitute cylindergroups, in another example, the cylinders are grouped based on firingorder considerations. For example, as shown in FIG. 4, cylinders 410,420, 422, and 416 constitute group 430, and cylinders 418, 412, 414, and424 constitute group 432. Note also that more than two groups ofcylinders may be used, if desired, and cylinder groups do not necessaryhave the same number of cylinders, although they may in one example.

FIG. 4 shows that each cylinder has three cylinder valves (a, b, and c).Thus, in this example, cylinder 410 has three valves, 410 a, 410 b, and410 c. Likewise, cylinder 412 has three valves, 412 a, 412 b, and 412 c,etc., up through cylinder 424 which has valves, 424 a, 424 b, and 424 c.While this example has three valves per cylinder, various otherconfigurations may be used, such as, for example, four valves percylinder, two valves per cylinder, or combinations thereof.

In the example of FIG. 4, each cylinder valve may be electricallyactuated without a camshaft. Alternatively, some of the cylinder valvesmay be electrically actuated and some may be cam actuated. The camactuated valves may have fixed cam timing, or may have variable camtiming. Further, the cam actuated valves may be mechanicallydeactivated, such as by deactivating a lifter or pushrod, for example.

FIG. 4 shows that each cylinder has two valves coupled to an intake sideof the engine (a, b) and one valve coupled to an exhaust side of theengine (c). As noted above, different numbers of valves may be used, forexample two intake side valves and two exhaust side valves. Further, asnoted above, some valves, such as intake side valves, can beelectrically actuated, while some valves, such as exhaust side valves,may be cam actuated. Also, FIG. 4 shows a split exhaust manifold (48 aand 48 b), however a common exhaust manifold may be used, if desired.Further, the split exhaust manifolds may form separate exhaust paths toatmosphere, or be joined together in a Y-pipe configuration. The joiningmay be upstream and/or downstream of emission control devices.

As will be described in more detail below, the cylinders may be groupedin various ways and numbers, and then the cylinders in one groupoperated in common and cylinders in another group also operated incommon, yet differently than those in the first group. For example,cylinders in group 320 can be operated with significantly retarded sparktiming (e.g., more than 5, 10, 15, 20, 25, 30, or more degrees later)than cylinders in group 322. Further, cylinders in group 320 can each beoperated with a different number or pattern of valves operating (ordeactivated, such as held closed during one or more (or all) strokes ofa combustion cycle) than group 322. For example, cylinders in group 320can operate with valves a and d (with valves b,c deactivated), whilecylinders in group 322 can operate with valves b and c (with valves a,ddeactivated), thereby providing a different pattern of active/de-activevalves. As another example, cylinders in group 320 can operate withvalves a, b and d (with valves c deactivated), while cylinders in group322 can operate with valves b and c (with valves a,d deactivated),thereby providing a different pattern and a different number ofactive/de-active valves.

In another embodiment, different patterns and/or number of valvesbetween the groups can be used under different conditions. For example,under a first set of conditions, cylinders in group 320 can operate withvalves a and c active (b,d deactivated) while cylinders in group 322operate with valves a, b, and d (c deactivated); and under a second setof conditions, cylinders in group 322 can operate with valves a and cactive (b,d deactivated) while cylinders in group 320 operate withvalves a, b, and d (c deactivated).

Such variable operation can be used to generate different amounts ofairflow and/or charge motion between different cylinders, therebyimproving conditions for the particular conditions of the differentcylinders. For example, cylinders operated with more retarded ignitiontiming may be operated with increased charge motion than other cylindersoperating with less retarded (or advanced) ignition timing. Also, whilethe above variations have been described with regard to FIG. 3, they mayalso be applied to the structure of FIG. 4. Further, various othermodifications and variations are possible, such as unequal cylindergroups (or a group of a single cylinder), and various alternativenumbers and/or patterns of valves. Further, cylinders within a group arenot necessarily operated with the same number and/or pattern of valves.For example, cylinders within a group can operated with differentactive/deactivated valves, and may vary such operation with operatingconditions.

As will be appreciated by one of ordinary skill in the art, the specificroutines described below in the flowcharts may represent one or more ofany number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various steps or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the disclosure, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used. Further, these Figures graphicallyrepresent code to be programmed into the computer readable storagemedium in controller 12.

Referring now to FIG. 5, a routine is described for controlling enginestarting operation. Specifically, in step 510, the routine determineswhether a cold start conditions is present. Such a condition may bebased one or more factors, such as whether engine coolant temperature(ECT) is below a threshold value, whether the engine has been soakingfor greater than a pre-selected time, whether catalyst temperature isbelow a threshold value, and/or combinations thereof or others. If so,the routine continues to step 512 to set a desired exhaust temperaturebase on cold starting conditions, such as those noted above. In oneexample, the routine may set a fixed desired exhaust temperature, whilein another example the routine may set a desired exhaust and/or catalysttemperature profile that varies with time or duration after a start.

Next, the routine continues to step 514 to determine whether a hotre-start condition may be present. Hot re-starts can be identified basedon similar parameters as a cold start, such as ECT and/or soak time. Ifthe answer to step 514 is yes, the routine continues to step 516 to setthe desired exhaust and/or catalyst temperature(s) based on the hotre-start conditions. As noted above, a variable profile may also beused, if desired.

In step 518, the routine determines whether a desulphurization isrequested and/or in progress. A desulphurization event includesoperating one or more emission control devices at an elevatedtemperature and with a selected air-fuel ratio (e.g., rich, lean, and/oroscillating lean and rich) to reduce contamination, such as sulphur(e.g. SOx) and/or other contaminants. Such a condition may be requestedby the routine based on an evaluation of emission control deviceperformance, and/or based on a fixed number or time of engine and/orvehicle operation. If the answer to step 518 is yes, the routinecontinues to step 520 where the routine sets the desired exhaust and/orcatalyst temperature(s) based on the de-SOx conditions. As noted above,a variable temperature profile may also be used, if desired.

Continuing with FIG. 5, in step 522 the routine sets the desiredtemperature based on operating conditions if not already set above. Notethat while a desired temperature, or temperature range may be set andused for exhaust and/or catalyst temperature control, it is alsopossible to set maximum and minimum temperature limits, above which (orbelow which) control is activated. However, within the limits, passivetemperature operation may be used. Further, only a minimum temperaturemay be set, and over-temperature (to some extent) tolerated depending onoperating conditions.

From step 522, the routine continues to step 524 to adjust engine and/orvehicle operation to increase heat if temperature is below the desiredtemperature and/or decrease heat if above the desired temperature. Asdescribed herein, various adjustments and/or mode variations may be usedto adjust the quantity and flux of heat in the exhaust gasses. Forexample, ignition timing retard of each cylinder in the engine may beused under some conditions, such as when the difference between thedesired and actual temperatures is within a pre-selected range. Further,variation in engine valve timing utilized to vary the amount of internalresiduals may also be used to affect exhaust temperature, along with theamount of engine flow, air-fuel ratio, idle speed set-point (when inidle speed control), and others. However, other adjustments may also beused in place of, or in addition to, the above. For example, the enginemay be operated with split ignition timing as described in more detailbelow herein with regard to FIG. 6. As another example, the engine canhave one or more cylinders vary the quantity of strokes in a combustioncycle, such as operate in two-cycle mode in order to double heat flux tothe exhaust. As yet another example, the engine can vary the combustionsequence (firing order) to preferentially provide selected exhaust in aselective manner to further increase heat generation and/or exhaustmixing. Additional details of this and other adjustments are includedherein below.

From step 524, the routine continues to step 526 where the routinedetermines whether conditions are present to transition out oftemperature control. For example, if a driver tips-in, the engine maydiscontinue or reduce various modes of operation, such as ignitiontiming retard, or others. A driver tip-in may be detected from enginepedal position, vehicle speed, manifold vacuum and/or others. If so, theroutine continues to step 528 to return engine operating conditions to abase mode.

Referring now to FIG. 6, a routine is described for selecting variousmodes of operation for adjusting the various operating parameters asdescribed above with regard to step 524. First, in step 610 the routinefirst determines whether one or more cylinders should be operated withdifferent ignition timing retard. For example, such operation may beenabled only after a predetermined number of combustion events haveoccurred, or after a certain engine coolant temperature has beenreached. In one embodiment, split ignition operation is enabled afterreaching a pre-selected engine coolant temperature. In anotherembodiment, split ignition operation is enabled after at least onecombustion event has occurred in each cylinder of the engine. In stillanother embodiment, split ignition operation is enabled after a firstcombustion event in any of the engine cylinders.

As described herein, one mode of operation that may be used is tooperation a first group of cylinders with ignition timing retardedsubstantially more than another group of cylinders (which may haveretarded or advanced ignition timing relative to top dead center (TDC).The difference in ignition timing may be more than 5 degrees, 8 degrees,10 degrees, 20 degrees, 25 degrees, or more. Such operation can increaseheat provided while still providing stable combustion and torque (orspeed) control. Further, in one example, the cylinders with moreretarded ignition timing produce significantly less torque, so that theremaining cylinders can operate at a higher load in order to make theoverall engine torque meet the desired torque. Also, the cylinders withless ignition timing retard can provide most of the engine output torqueand thereby control engine torque or idle speed, while the othercylinders with more retard generate even greater heat. Further still,since the engine is operating at a higher load, better airflow controlcan be achieved. In other words, since the change in throttle position(or valve timing) to change in airflow slope can be decreased at higherload, improved controllability may be achieved.

In one particular embodiment, the routine can set the ignition timing ofa first and second cylinder groups to differing values. Specifically,the ignition timing for the first group can be set equal to a maximumtorque, or best torque, timing (MBT), or to an amount of ignition retardthat still provides good combustion for powering and controlling theengine. Further, the ignition timing for the second group can be setequal to a significantly retarded valued, for example −29 degrees ormore. Note that various other values can be used in place of the 29degrees value depending on engine configuration, engine operatingconditions, and various other factors. Note that various other amountsof retard may be used, such as between 0-5 degrees after top dead center(TDC), 5-20 degrees after TDC, 5-35 degrees after TDC, or others.

Also, the amount of ignition timing retard for the second group can varybased on engine operating parameters, such as air-fuel ratio, engineload, and engine coolant temperature, or catalyst temperature (i.e., ascatalyst temperature rises, less retard in the first and/or second groupmay be desired). Further, the combustion stability limit value can alsobe a function of these parameters. Also note that the first cylindergroup ignition timing does not necessarily have to be set to maximumtorque ignition timing. Rather, it can be set to a less retarded valuethan the second cylinder group, if such conditions provide acceptableengine torque control and acceptable vibration. That is, it can be setto the combustion stability spark limit (e.g., −10 degrees). In thisway, the cylinders on the first group operate at a higher load than theyotherwise would if all of the cylinders were producing equal engineoutput. In other words, to maintain a certain engine output (forexample, engine speed, engine torque, etc.) with some cylindersproducing more engine output than others, the cylinders operating at thehigher engine output produce more engine output than they otherwisewould if all cylinders were producing substantially equal engine output.As an example, if there is a four cylinder engine and all cylinders areproducing a unitless output of 1, then the total engine output is 4.Alternatively, to maintain the same engine output of 4 with somecylinders operating at a higher engine output than others, then, forexample, two cylinders would have an output of 1.5, while the other twocylinders would have an output of 0.5, again for a total engine outputof 4. Thus, by operating some cylinders at a more retarded ignitiontiming than others, it is possible to place some of the cylinders into ahigher engine load condition. This allows the cylinders operating at thehigher load to tolerate additional ignition timing retard (or additionalenleanment), if desired. Thus, in such examples, the cylinders operatingwith a unitless engine output of 1.5 could tolerate significantly moreignition timing retard than if all of the cylinders were operating at anengine output of 1. In this way, additional heat may be provided to theengine exhaust to heat the emission control device.

An advantage to the above aspect is that more heat can be created byoperating some of the cylinders at a higher engine load withsignificantly more ignition timing retard than if operating all of thecylinders at substantially the same ignition timing retard, at leastunder some conditions. Further, by selecting the cylinder groups thatoperate at the higher load, and the lower load, it is possible to reduceengine vibration. Thus, in one embodiment, the engine starts by firingcylinders from both cylinder groups. Then, the ignition timing of thecylinder groups is adjusted differently to provide rapid heating, whileat the same time providing good combustion and control.

Also note that the above operation can provide additional heat to boththe first and second cylinder groups since the cylinder group operatingat a higher load generates more heat flux to the catalyst, while thecylinder group operating with more retard operates at a hightemperature. Also, when operating with a system of the configurationshown in FIG. 4 (for example a V-8 engine), the two banks aresubstantially equally heated since each catalyst is receiving gassesfrom both the first and second cylinder groups.

However, when using such an approach with a V-10 engine (where the banksconstitute cylinder groups) the cylinder groups provide exhaust only todifferent banks of catalyst. As such, one bank may heat to a differenttemperature than the other. In this case, operation may be modified soperiodically (for example, after a predetermined time period, or numberof engine revolutions, etc.) the cylinder group operation is switched.In other words, if the routine starts with the first group operatingwith more retard than the second group, then after said duration, thesecond group is operated with more retard than the first, and so on. Inthis way, even heating of the exhaust system is achieved.

Also note that all of the cylinders in the first cylinder group do notnecessarily operate at exactly the same ignition timing. Rather, therecan be small variations (for example, several degrees) to account forcylinder to cylinder variability. This is also true for all of thecylinders in the second cylinder group (and the first group). Further,in general, there can be more than two cylinder groups, and the cylindergroups can have only one cylinder. However, in one specific example of aV8, configured as in FIG. 4, there are 2 groups, with four cylinderseach. Further, the cylinder groups can be two or more.

Furthermore, the engine cylinder air-fuel ratios can be set at differentlevels. In one particular example, all the cylinders are operatedsubstantially at stoichiometry. In another example, all the cylindersare operated slightly lean of stoichiometry. In still another example,the cylinders with more ignition timing retard are operated slightlylean of stoichiometry, and the cylinders with less ignition timingretard are operated slightly rich of stoichiometry. Further, in stillanother example, the overall mixture air-fuel ratio is set to beslightly lean of stoichiometry. In other words, the lean cylinders withthe greater ignition timing retard are set lean enough such that thereis more excess oxygen than excess rich gasses of the rich cylindergroups operating with less ignition timing retard.

In an alternative embodiment, two different catalyst heating modes maybe provided. In the first mode, the engine operates with some cylindershaving more ignition timing retard than others. As described above, thisallows the cylinders to operate at substantially higher load (forexample, up to 70% air charge), since the cylinders with more retard areproducing less torque. Thus, the cylinders with less retard than otherscan actually tolerate more ignition timing retard than if all cylinderswere operating with substantially the same ignition timing retard whileproviding stable combustion, at least under some conditions. Then, theremaining cylinders produce large amounts of heat, and the unstablecombustion has minimal NVH (Noise, Vibration, Harshness) impacts sincevery little torque is being produced in those cylinders. In this firstmode, the air-fuel ratio of the cylinders can be set slightly lean ofstoichiometry, or other values as described above. In a second mode, theengine operates with all of the cylinders having substantially the sameignition timing, which is retarded to near the combustion stabilitylimit. While this provides less heat, it may provide increased fueleconomy. Further, the engine cylinders are operated near stoichiometry,or slightly lean of stoichiometry. In this way, after engine start-up,maximum heat is provided to the catalyst by operating the engine in thefirst mode until, for example, a certain time elapses, or a certaintemperature is reached. Then, the engine is transitioned to operatingwith all cylinders having substantially the same ignition timing retard.Then, once the catalyst has reached a higher temperature, or anotherprescribed time period has passed, the engine is transitioned tooperating near optimal ignition timing.

In addition to the above variations, operating with one group ofcylinders having ignition timing more, or significantly more, retardedthan another group of cylinders can be combined with variations in valvetiming, valve lift, numbers of active valves, valve patterns, and moreto provide still other advantages. For example, the torque imbalancebetween the cylinder groups can be partially offset, or exaggerated(whichever is desired) by varying valve timing between the cylindergroups, such as with electrically actuated valves. In other words, thecylinders with less ignition timing retard can be operated with less (ormore) fresh airflow by varying at least one of an intake valve openinglocation and/or an intake valve closing location than that of valves inthe cylinders with more ignition timing retard. Further, the cylindergroups can be operated with differing amounts of residual gasses in thechamber by varying at least one of intake valve opening and/or exhaustvalve closing (e.g., by varying overlap). For example, the firstcylinder group may be operated with more (or less) valve overlap thananother group of cylinders by varying timing of electrically actuatedvalves. Such operation can be used to optimize the valve timing for thedifferent cylinder groups and tailor the valve timing to the specificcombustion characteristics between the groups.

As another example, the number of active (or deactivated) valves orpatterns of valves may be varied between the cylinder groups. In otherwords, the cylinder group with more retarded ignition timing may beoperated with more (or less) active valves (or different valve patterns)to further vary the cylinder charge between cylinder group, and/or tovary cylinder motion between group. Such operation can improvecombustion performance of the different groups to increase heatgeneration or improve burn characteristics and combustion stability.

As still another example, the number of cylinders in respective cylindergroups may be varied to vary heat generation and/or torque capacity.Also, the number of strokes in the cylinder groups may be varied toincrease heat generation and/or torque capacity. For example, a group ofcylinders with more retarded ignition timing than another group ofcylinders can be operated with less strokes per combustion cycles (e.g.,2-stroke) to increase heat flux. Further, the valve timing of thecylinders operating with a different number of strokes can be varied toreduce the effects of operating with other than a four-stroke combustioncycle.

Returning to step 610, if disparate ignition timing operation isrequested, the routine continues to step 612 where it is determinewhether increased exhaust mixing between the cylinder groups is desired.If so, the routine continues to step 614 to select a firing order. If afiring order change is requested (e.g., the selected firing order isdifferent from the current firing order), the routine continues to step616 to change the firing order. Then, the routine continues to step 618to increase and/or decrease a number of strokes on selected cylindersfor a number of strokes, or combustion cycles, until the desired firingorder is obtained. Note that more than one cylinder may be selected tovary its number of strokes, and in such a case the cylinders can havetheir strokes increased concurrently or serially, or combinationsthereof. Further, under variable conditions, different cylinders may beselected to increase and/or decrease the number of strokes to vary thecombustion sequence.

Thus, in one example, all of the engine cylinders may be operating in afour-stroke combustion cycle. Then, one or more cylinders can beoperated with an increase or decreased number of strokes (e.g.,2-stroke, 6-stroke) for one or more cycles until the new desired firingorder is achieved. At that point, the cylinders with increased/decreasedstrokes can be returned to four-stroke operation.

Another example where variation in exhaust mixing may be used relates toa V-8 engine, where the firing may not be bank-to-bank. For example, aV-8 engine may have a firing order of 1-5-4-2-6-3-7-8 (where cylinder 1corresponds to cylinder 410 of FIG. 4, cylinder 2 corresponds tocylinder 412, and so on up to cylinder 8 corresponding to cylinder 418).Further, the bank sequence firing is R-L-R-R-L-R-L-L (where Rcorresponds to a right bank and L corresponds to a left bank). In splitignition operation, four cylinders produce a majority of the enginetorque (denoted as “P” cylinders) and the other four produce very littletorque but large amounts of heat (denoted as “H” cylinders).

In one embodiment, for smoother engine operation, the firing of thecylinders should alternate, such as the firing is P-H-P-H-P-H-P-H. Inother words, below a selected speed, for example, the engine is operatedwith the above firing order to reduce NVH issues, while still providingthe desired engine torque and exhaust heat.

However, under other operating conditions (e.g., above a selected enginespeed), for improved exhaust mixing, the firing order may be varied,where two cylinders (e.g., both cylinders 3 and 5, which are H cylindersand therefore produce very little torque), are operated in a differentfiring sequence, where the cylinders can be switched at the onset of thesplit ignition mode, for example, and switched back after the catalysthas reached a set temperature, since they are producing reduced enginetorque. Thus, in one mode, the two banks will fire as follows:

Right Bank—P-x-P-H-x-H-x-x

Left Bank—x-H-x-x-P-x-P-H

Then, in another mode, cylinders 3 and 5, for example, will be switchedso that the engine will fire as follows (e.g., a firing order of1-3-4-2-6-5-7-8):

Right Bank—P-H-P-H-x-x-x-x

Left Bank—x-x-x-x-P-H-P-H

In this way, improved mixing on each bank can be achieved, in that therewill be better mixing of the exhaust from the P and H strokes which canresult in faster heating of the catalyst with improved post flameoxidation of hydrocarbons (HC). Further, as noted above, the cylinderfiring order may be switched by increasing/decreasing a number ofstrokes in one or more cylinders.

In another embodiment, the engine can be started with a first firingorder and then switched to a different firing order once a predeterminedexhaust and/or catalyst temperature has been reached, for example. Inother words, during a cold start, the engine can start in split ignitionoperation with cylinders 3 and 5, for example, already in an alternatefiring order for improved mixing. Then, each of cylinders 3 and 5 can beoperated for a single cycle (or more) with an increased number ofstrokes (e.g., six-stroke, with double compression, double exhaust,double intake, etc.) to switch prior to ending split ignition operation.

In still another embodiment, improved starting time may be achieved bystarting with all cylinders firing with substantially similar ignitiontiming, and then switching two cylinders using a six-stroke mode (e.g.,with multiple exhaust strokes, having valves opened or closed).

Note that when increasing a number of strokes to changing firing order,there may be a small torque deficiency due to the temporary six-strokeoperation. However, since in one embodiment the two cylinders beingadjusted are producing reduced torque, there such a decrease may beneglected. The torque deficiency may also be compensated by temporarilyincreasing torque of other cylinders currently firing whenmulti-stroking the cylinders to mask any torque disturbance. Further,the torque hole can be decreased by trapping most of the exhaust for the4th, 5th and 6th strokes.

Referring now to FIG. 7 and continuing with a description of additionalaspects of the control routines described herein, there are variouscontrol actions for increasing/decreasing exhaust/catalyst temperatureand increasing/decreasing engine torque, such as selected in step 524.As noted above, various methods may be selected and/or combined undervarious operating conditions to achieve advantageous operation. Forexample, one or more of the following adjustments may be used alone orin combination to adjust exhaust temperature:

-   -   adjusting ignition timing of cylinders with ignition timing        retard significantly more than other cylinders;    -   varying a number of cylinders with retarded ignition timing;    -   varying air amounts between cylinder groups (e.g., between        groups with more or less ignition timing retard);    -   varying spark timing of cylinders with significant retard;    -   varying a number of cylinders operating in 2-stroke mode;    -   varying a number of exhaust valves active in a cylinder;    -   varying exhaust valve and/or intake valve timing of cylinders        and/or between cylinder groups;    -   varying a pattern of valves between cylinder groups;    -   varying firing order;    -   varying engine throttle;    -   varying engine idle speed; and    -   others.

As described herein, the above approaches may be used in combination toachieve certain advantageous operation. Further, since some of theseactions may affect engine torque, various other adjustments may be usedto balance engine torque output during such adjustments. These mayinclude:

-   -   adjusting spark timing cylinders with less spark retard    -   adjusting a number of cylinders with more/less spark retard    -   adjusting air and/or fuel amounts to cylinders with less spark        retard;    -   adjusting a number of intake valves active on cylinders with        less spark retard;    -   adjusting exhaust valve and/or intake valve timing of cylinders        and/or between cylinder groups;    -   adjusting valve lift of cylinders with less spark retard;    -   adjusting engine throttle; and    -   others.

However, in one example where split ignition timing is used, adjustmentsmade to cylinders with greater spark retard can have a minimal impact onengine torque, and thus only small adjustments may be needed to maintainoverall engine torque.

Continuing with FIG. 7, in step 710 the routine determines an adjustmentto one or more of the above parameters to adjust exhaust temperature.Then, in step 712, the routine determines if any adjustment is necessaryto compensate for a torque change caused by the adjustment determined instep 710. If so, the routine continues to step 714 to determine anadjustment to adjust engine torque to the desired value and counteractany torque affect of the increased/decreased exhaust heating. Then, theroutine continues to step 718 to adjust parameters as determined insteps 710 and 714/716.

Referring now to FIGS. 8-11, several engine timing diagrams illustratevarious alternative embodiments of the operation described herein, showsintake valve timing (I), exhaust valve timing (E), fuel injection (inj)and ignition/spark timing (spk). The x-axis illustrated engine/pistonposition assuming a four-stroke combustion cycle (which may not be theactual case, such as described below), with 0 degrees indicating TDC ofa compression for such an assumed cycle.

FIG. 8 shows an I-4 example where cylinders 1 and 4 form a first groupand cylinders 2 and 3 form a second group, such as shown in FIG. 3, forexample. Alternatively, FIG. 8 may show one bank of a V-8 engine. FIG. 8shows a port fuel injected example where different valve timings areused between the cylinder groups operating with split ignition timing,and where each cylinder has one intake valve and one exhaust valve.Further, the fuel injection is varied between the cylinders so that bothcylinders operate with an air-fuel ratio about stoichiometry.Specifically, cylinders 1 and 4 operate with less ignition timing retardthan cylinders 2 and 3. Further, cylinders 1 and 4 operate withincreased cylinder air charge (due to longer intake valve opening), withcorrespondingly more injected fuel.

FIG. 9 shows an example similar to that of FIG. 8, except thatmulti-stroke operation is shown where cylinder 2 operates in a 2-strokemode to increase heat flux. Again, different valve timings are utilizedbetween cylinder groups, where the valve timing of cylinder 2 may beadjusted so that improved 2-stroke operation is achieved.

FIG. 10 shows an example similar to that of FIG. 8, except that eachcylinder has two intake valve and one exhaust valve. FIG. 9 also showsvariation in valve timing between the cylinder groups, and also showshow valve timing between two intake valves in a given cylinder may bevaried (e.g., to increase charge motion). It also illustrates how somecylinder groups may use staggered cylinder valve timing while othercylinder groups operate two intake valves with equal timing). In thisway, charge motion suited to the different combustion in the cylindergroups may be achieved.

FIG. 11 shows another example similar to that of FIG. 8, except thateach cylinder has two intake valve and one exhaust valve. FIG. 11 alsoshows variation in valve timing between the cylinder groups, as well ashow a different number of valves between cylinder groups may be used toadvantage.

While the above figures show several variations, numerous others arepossible.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above approaches can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. Also, the approachesdescribed above are not specifically limited to a dual coil valveactuator. Rather, it could be applied to other forms of actuators,including ones that have only a single coil per valve actuator, and/orother variable valve timing systems, such as, for example, cam phasing,cam profile switching, variable rocker ratio, etc.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various systems andconfigurations, and other features, functions, and/or propertiesdisclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A method for operating an engine having at least a first and secondcylinder, comprising: operating the first cylinder with a spark timingmore retarded than a spark timing of a second cylinder; and operatingone of said first cylinder and second cylinder with a first number ofstrokes per cycle different from other cylinders of the engine for atleast one combustion cycle, wherein said first cylinder is operated witha first number of strokes per cycle, and said second cylinder isoperated with a second number of strokes per cycle greater than saidfirst number.
 2. The method of claim 1 wherein said first cylinderincludes 2-stroke operation and said second cylinder includes 4-strokeoperation.
 3. The method of claim 1 wherein said operation with saiddifferent number of strokes is performed temporarily to transition theengine from a first firing order to a second firing order different fromsaid first firing order.
 4. The method of claim 3 wherein more than onecylinder is operated with said first number of strokes.
 5. A method foroperating an engine having at least a first and second cylinder,comprising: operating the first cylinder with a spark timing moreretarded than a spark timing of a second cylinder; and operating one ofsaid first cylinder and second cylinder with a first number of strokesper cycle different from other cylinders of the engine for at least onecombustion cycle, wherein said operation with more retarded spark timingis performed before said operation with different a different number ofstrokes.
 6. A method for operating an engine having at least a first andsecond cylinder, comprising: operating the first cylinder with a sparktiming more retarded than a spark timing of a second cylinder; andoperating one of said first cylinder and second cylinder with a firstnumber of strokes per cycle different from other cylinders of the enginefor at least one combustion cycle, wherein said operation with moreretarded spark timing is performed after said operation with different adifferent number of strokes.
 7. A method for operating an engine havingat least a first and second cylinder, comprising: operating the firstcylinder with a spark timing more retarded than a spark timing of asecond cylinder, where during said operation, said first cylinderoperates with a first number of strokes per cycles and said secondcylinder operates with a second number of strokes per cycle, where saidfirst number is different from said second number, wherein the firstcylinder operates with a spark timing substantially more retarded than aspark timing of a second cylinder, and wherein a difference between saidspark timing of the first and second cylinders is more than 8 degrees.8. The method of claim 7 wherein said first number of strokes is two,and said second number of strokes is four.
 9. The method of claim 8wherein said operation is carried out when adjusting a firing order ofthe engine during engine operation.
 10. The method of claim 8 whereinsaid operation is performed during at least some engine cold startingconditions after at least one combustion event in each cylinder of theengine.
 11. The method of claim 10 wherein said first cylinder operateswith valve timing different from said second cylinder.
 12. The method ofclaim 11 wherein more than one cylinder operates with a two-strokecombustion cycle.
 13. The method of claim 11 wherein more than onecylinder operates with a two-stroke combustion cycle serially whenchanging firing order.
 14. The method of claim 11 wherein more than onecylinder operates with a two-stroke combustion cycle simultaneously whenchanging firing order.
 15. A method for operating an engine having atleast a first and second cylinder, comprising: operating the firstcylinder with a spark timing more retarded than a spark timing of asecond cylinder, where during said operation, said first cylinderoperates temporarily with a first number of strokes per cycle and saidsecond cylinder operates with a second number of strokes per cycle,where said first number is different from said second number to change afiring order of the engine, and then said first cylinder operates withsaid second number of strokes, wherein under different operatingconditions, a third cylinder operating with a spark timing more retardedthan said timing of said second cylinder is operated with a number ofstrokes per cycle different from said second number of strokes to changea firing order of the engine.
 16. The method of claim 15 wherein adifference between said spark timing of the first and second cylindersis more than 8 degrees.
 17. The method of claim 15 wherein said firstnumber of strokes is two, and said second number of strokes is four. 18.The method of claim 15 wherein said operation is performed during atleast some engine cold starting conditions after at least one combustionevent in each cylinder of the engine.